يرصبلا), after his birthplace in the city of Basra. [5]He was also nicknamed Ptolemaeus Secundus ("Ptolemy the Second") [6]or simply "The Physicist" [7]in medieval Europe.

Born circa 965, in Basra, part of present-day Iraq and part of Buyid Persia at that time, [1]he lived mainly in Cairo, Egypt, dying there at age 76. [6]Over-confident about practical application of his mathematical knowledge, he assumed that he could regulate the floods of the Nile. [8]After being ordered by Al-Hakim bi-Amr Allah, the sixth ruler of the Fatimid caliphate, to carry out this operation, he quickly perceived the impossibility of what he was attempting to do, and retired from engineering. Fearing for his life, he feigned madness [1][9]and was placed under house arrest, during and after which he devoted himself to his scientific work until his death. [6]

Although there are stories that Ibn al-Haytham fled to Syria, ventured into Baghdad later in his life, or was even in Basra when he pretended to be insane, it is certain that he was in Egypt by 1038 at the latest. [5]During his time in Cairo, he became associated with Al-Azhar University, as well the city's "House of Wisdom", [39]known as Dar Al-Hekma (House of Knowledge), which was a library "second in importance" to Baghdad's House of Wisdom. [5]After his house arrest ended, he wrote scores of other treatises on physics, astronomy and mathematics. He later traveled to Islamic Spain. During this period, he had ample time for his scientific pursuits, which included optics, mathematics, physics, medicine, and the development of scientific methods; he left several outstanding books on these subjects.

Ibn al-Haythem made significant improvements in optics, physical science, and the scientific method which influenced the development of science for over five hundred years after his death. Ibn al-Haytham's work on optics is credited with contributing a new emphasis on experiment. His influence on physical sciences in general, and on optics in particular, has been held in high esteem and, in fact, ushered in a new era in optical research, both in theory and practice. [11]The scientific method is considered to be so fundamental to modern science that some—especially philosophers of science and practising scientists—consider earlier inquiries into nature to be pre-scientific. [40]

Richard Powers nominated Ibn al-Haytham's scientific method and scientific skepticism as the most influential idea of the second millennium. [35]Recipient of the Nobel Prize in Physics Abdus Salam considered Ibn-al-Haytham "one of the greatest physicists of all time." [28]George Sarton, the father of the history of science, wrote that "Ibn Haytham's writings reveal his fine development of the experimental faculty" and considered him "not only the greatest Muslim physicist, but by all means the greatest of mediaeval times." [41]Robert S. Elliot considers Ibn al-Haytham to be "one of the ablest students of optics of all times." [42]The author Bradley Steffens considers him to be the "first scientist", [43]and Professor Jim Al- Khalili also considers him the "world's first true scientist". [44]The Biographical Dictionary of Scientists wrote that Ibn al-Haytham was "probably the greatest scientist of the Middle Ages" and that "his work remained unsurpassed for nearly 600 years until the time of Johannes Kepler." [45]At a scientific conference in February 2007 as a part of the Hockney-Falco thesis, Charles M. Falco argued that Ibn al-Haytham's work on optics may have influenced the use of optical aids by Renaissance artists. Falco said that his and David Hockney's examples of Renaissance art "demonstrate a continuum in the use of optics by artists from circa 1430, arguably initiated as a result of Ibn al-Haytham's influence, until today." [46]

Meanwhile in the Islamic world, Ibn al-Haytham's work influenced Averroes' writings on optics, [48]and his legacy was further advanced through the 'reforming' of his Optics by Persian scientist Kamal al-Din al-Farisi (d. ca. 1320) in the latter's Kitab Tanqih al-Manazir (The Revision of [Ibn al-Haytham's] Optics). [22][49]The correct explanations of the rainbow phenomenon given by al-Fārisī and Theodoric of Freiberg in the 14th century depended on

Ibn al-Haytham's Book of Optics. [50]The work of Ibn al-Haytham and al-Fārisī was also further advanced in the Ottoman Empire by polymath Taqi al-Din in his Book of the Light of the Pupil of Vision and the Light of the Truth of the Sights (1574). [51]

He wrote around 200 books, although very few have survived. Even some of his treatises on optics survived only through Latin translation. During the Middle Ages his books on cosmology were translated into Latin, Hebrew and other languages.

The crater Alhazen on the Moon is named in his honour [16], as was the asteroid "59239 Alhazen". [52]Ibn al-Haytham is featured on the obverse of the Iraqi 10,000 dinars banknote issued in 2003, [53]and on 10 dinar notes from 1982. A research facility that UN weapons inspectors suspected of conducting chemical and biological weapons research in Saddam Hussein's Iraq was also named after him. [53][54]

Optics was translated into Latin by an unknown scholar at the end of the 12th century or the beginning of the 13th century. [56]It was printed by Friedrich Risner in 1572, with the title Opticae thesaurus: Alhazeni Arabis libri septem, nuncprimum editi; Eiusdem liber De Crepusculis et nubium ascensionibus. [57]Risner is also the author of the name variant "Alhazen"; before Risner he was known in the west as Alhacen, which is the correct transcription of the Arabic name. [58]This work enjoyed a great reputation during the Middle Ages. Works by Ibn al-Haytham on geometric subjects were discovered in the Bibliothèque nationale in Paris in 1834 by E. A. Sedillot. Other manuscripts are preserved in the Bodleian Library at Oxford and in the library of Leiden.

The work of Ibn al-Haytham and al-Fārisī was also further advanced in the Ottoman Empire by polymath Taqi al-Din in his Book of the Light of the Pupil of Vision and the Light of the Truth of the Sights (1574). He wrote around 200 books, although very few have survived. Even some of his treatises on optics survived only through Latin translation. During the Middle Ages his books on cosmology were translated into Latin, Hebrew and other languages. The crater Alhazen on the Moon is named in his honou r , as was the asteroid "59239 Alhazen ". Ibn al-Haytham is featured on the obverse of the Iraqi 10,000 dinars banknote issued in 2003 , and on 10 dinar notes from 1982. A research facility that UN weapons inspectors suspected of conducting chemical and biological weapons research in Saddam Hussein's Iraq was also named after him. [edit] Book of Optics Main article: Book of Optics Ibn al-Haytham's most famous work is his seven volume Arabic treatise on optics , Kitab al- Manazir ( Book of Optics ), written from 1011 to 1021. It has been ranked alongside Isaac Newton' s Philosophiae Naturalis Principia Mathematica as one of the most influential books in physic s for introducing an early scientific method, and for initiating a revolution in optic s and visual perception . Optics was translated into Latin by an unknown scholar at the end of the 12th century or the beginning of the 13th century. It was printed by Friedrich Risner in 1572, with the title Opticae thesaurus: Alhazeni Arabis libri septem, nuncprimum editi; Eiusdem liber De Crepusculis et nubium ascensionibus . Risner is also the author of the name variant "Alhazen"; before Risner he was known in the west as Alhacen, which is the correct transcription of the Arabic name. This work enjoyed a great reputation during the Middle Ages . Works by Ibn al-Haytham on geometric subjects were discovered in the Bibliothèque nationale in Paris in 1834 by E. A. Sedillot. Other manuscripts are preserved in the Bodleian Library at Oxford and in the library of Leiden . [edit] Optics Ibn al-Haytham proved that light travels in straight lines using the scientific method in his Book of Optics (1021). Two major theories on vision prevailed in classical antiquity . The first theory, the emission theory , was supported by such thinkers as Euclid and Ptolemy, who believed that sight worked by the eye emitting rays of light . The second theory, the intromission theory supported by Aristotle and his followers, had physical forms entering the eye from an object. Ibn al-Haytham argued that the process of vision occurs neither by rays emitted from the eye, nor through physical forms entering it. He reasoned that a ray could not proceed from the eyes and reach the distant stars the instant after we open our eyes. He also appealed to common observations such as the eye being dazzled or even injured if we look at a very bright light. He instead developed a highly successful theory which explained the process of vision as rays of light proceeding to the eye from each point on an object, which he proved " id="pdf-obj-5-112" src="pdf-obj-5-112.jpg">

Two major theories on vision prevailed in classical antiquity. The first theory, the emission theory, was supported by such thinkers as Euclid and Ptolemy, who believed that sight worked by the eye emitting rays of light. The second theory, the intromission theory supported by Aristotle and his followers, had physical forms entering the eye from an object. Ibn al-Haytham argued that the process of vision occurs neither by rays emitted from the eye, nor through physical forms entering it. He reasoned that a ray could not proceed from the eyes and reach the distant stars the instant after we open our eyes. He also appealed to common observations such as the eye being dazzled or even injured if we look at a very bright light. He instead developed a highly successful theory which explained the process of vision as rays of light proceeding to the eye from each point on an object, which he proved

Ibn al-Haytham proved that rays of light travel in straight lines, and carried out various experiments with lenses, mirrors, refraction, and reflection. [11]He was also the first to reduce reflected and refracted light rays into vertical and horizontal components, which was a fundamental development in geometric optics. [61]He also discovered a result similar to Snell's law of sines, but did not quantify it and derive the law mathematically. [62]

Ibn al-Haytham also gave the first clear description [26]and correct analysis [27]of the camera obscura and pinhole camera. While Aristotle, Theon of Alexandria, Al-Kindi (Alkindus) and Chinese philosopher Mozi had earlier described the effects of a single light passing through a pinhole, none of them suggested that what is being projected onto the screen is an image of everything on the other side of the aperture. Ibn al-Haytham was the first to demonstrate this with his lamp experiment where several different light sources are arranged across a large area. He was thus the first to successfully project an entire image from outdoors onto a screen indoors with the camera obscura. [63]

His most original anatomical contribution was his description of the functional anatomy of the eye as an optical system, [70]or optical instrument. His experiments with the camera obscura provided sufficient empirical grounds for him to develop his theory of corresponding point projection of light from the surface of an object to form an image on a screen. It was his comparison between the eye and the camera obscura which brought about his synthesis of anatomy and optics, which forms the basis of physiological optics. As he conceptualized the essential principles of pinhole projection from his experiments with the pinhole camera, he considered image inversion to also occur in the eye, [64]and viewed the pupil as being similar to an aperture. [71]Regarding the process of image formation, he incorrectly agreed with Avicenna that the lens was the receptive organ of sight, but correctly hinted at the retina being involved in the process. [68]

Neuroscientist Rosanna Gorini notes that "according to the majority of the historians al- Haytham was the pioneer of the modern scientific method." [16][72]Ibn al-Haytham developed rigorous experimental methods of controlled scientific testing to verify theoretical hypotheses and substantiate inductive conjectures. [30]Ibn al-Haytham's scientific method was very similar to the modern scientific method and consisted of the following procedures: [73]

An aspect associated with Ibn al-Haytham's optical research is related to systemic and methodological reliance on experimentation (i'tibar) and controlled testing in his scientific inquiries. Moreover, his experimental directives rested on combining classical physics ('ilm

tabi'i) with mathematics (ta'alim; geometry in particular) in terms of devising the rudiments of what may be designated as a hypothetico-deductive procedure in scientific research. This mathematical-physical approach to experimental science supported most of his propositions in Kitab al-Manazir (The Optics; De aspectibus or Perspectivae) and grounded his theories of vision, light and colour, as well as his research in catoptrics and dioptrics (the study of the refraction of light). His legacy was further advanced through the 'reforming' of his Optics by Kamal al-Din al-Farisi (d. ca. 1320) in the latter's Kitab Tanqih al-Manazir (The Revision of [Ibn al-Haytham's] Optics). [22][49]

The concept of Occam's razor is also present in the Book of Optics. For example, after demonstrating that light is generated by luminous objects and emitted or reflected into the eyes, he states that therefore "the extramission of [visual] rays is superfluous and useless." [74]

His work on catoptrics in Book V of the Book of Optics contains a discussion of what is now known as Alhazen's problem, first formulated by Ptolemy in 150 AD. It comprises drawing lines from two points in the plane of a circle meeting at a point on the circumference and making equal angles with the normal at that point. This is equivalent to finding the point on the edge of a circular billiard table at which a cue ball at a given point must be aimed in order to canon off the edge of the table and hit another ball at a second given point. Thus, its main application in optics is to solve the problem, "Given a light source and a spherical mirror, find the point on the mirror were [sic] the light will be reflected to the eye of an observer." This leads to an equation of the fourth degree. [5][75]This eventually led Ibn al-Haytham to derive the earliest formula for the sum of fourth powers; by using an early proof by mathematical induction, he developed a method that can be readily generalized to find the formula for the sum of any integral powers. He applied his result of sums on integral powers to find the volume of a paraboloid through integration. He was thus able to find the integrals for polynomials up to the fourth degree, and came close to finding a general formula for the integrals of any polynomials. This was fundamental to the development of infinitesimal and integral calculus. [33]Ibn al-Haytham eventually solved the problem using conic sections and a geometric proof, though many after him attempted to find an algebraic solution to the problem, [32]which was finally found in 1997 by the Oxford mathematician Peter M. Neumann. [76]

Chapters 15–16 of the Book of Optics covered astronomy. Ibn al-Haytham was the first to discover that the celestial spheres do not consist of solid matter. He also discovered that the heavens are less dense than the air. These views were later repeated by Witelo and had a significant influence on the Copernican and Tychonic systems of astronomy. [77]

In Islamic psychology, Ibn al-Haytham is considered the founder of experimental psychology by A. I. Sabra, [21]for his pioneering work on the psychology of visual perception and optical illusions. [22]In the Book of Optics, Ibn al-Haytham was the first scientist to argue that vision occurs in the brain, rather than the eyes. He pointed out that personal experience has an effect on what people see and how they see, and that vision and perception are subjective. [22]

He came up with a theory to explain the Moon illusion, which played an important role in the scientific tradition of medieval Europe. It was an attempt to the solve the problem of the Moon appearing larger near the horizon than it does while higher up in the sky. Arguing

against Ptolemy's refraction theory, he redefined the problem in terms of perceived, rather than real, enlargement. He said that judging the distance of an object depends on there being an uninterrupted sequence of intervening bodies between the object and the observer. With the Moon however, there are no intervening objects. Therefore, since the size of an object depends on its observed distance, which is in this case inaccurate, the Moon appears larger on the horizon. Through works by Roger Bacon, John Pecham and Witelo based on Ibn al- Haytham's explanation, the Moon illusion gradually came to be accepted as a psychological phenomenon, with Ptolemy's theory being rejected in the 17th century. [79]

Omar Khaleefa has argued that Ibn al-Haytham should also be considered the founder of psychophysics, a subdiscipline and precursor to modern psychology. [21]Although Ibn al- Haytham made many subjective reports regarding vision, there is no evidence that he used quantitative psychophysical techniques and the claim has been rebuffed. [80]

In his treatise, Mizan al-Hikmah (Balance of Wisdom), Ibn al-Haytham discussed the density of the atmosphere and related it to altitude. He also studied atmospheric refraction. He discovered that the twilight only ceases or begins when the Sun is 19° below the horizon and attempted to measure the height of the atmosphere on that basis. [11]

Another treatise, Maqala fi daw al-qamar (On the Light of the Moon), which he wrote some time before his famous Book of Optics, was the first successful attempt at combining mathematical astronomy with physics, and the earliest attempt at applying the experimental method to astronomy and astrophysics. He disproved the universally held opinion that the Moon reflects sunlight like a mirror and correctly concluded that it "emits light from those portions of its surface which the sun's light strikes." To prove that "light is emitted from every point of the Moon's illuminated surface," he built an "ingenious experimental device." [83]According to Matthias Schramm, Ibn al-Haytham had

formulated a clear conception of the relationship between an ideal mathematical model and the complex of observable phenomena; in particular, he was the first to make a systematic use of the method of varying the experimental conditions in a constant and uniform manner, in an experiment

showing that the intensity of the light-spot formed by the projection of the moonlight through two small apertures onto a screen diminishes constantly as one of the apertures is gradually blocked up. [83]

Also in his Treatise on Place, Ibn al-Haytham disagreed with Aristotle's view that nature abhors a void, and he thus used geometry to demonstrate that place (al-makan) is the imagined three-dimensional void between the inner surfaces of a containing body. [84]

In his Al-Shukūk ‛alā Batlamyūs, variously translated as Doubts Concerning Ptolemy or Aporias against Ptolemy, published at some time between 1025 and 1028, Ibn al-Haytham criticized many of Ptolemy's works, including the Almagest, Planetary Hypotheses, and Optics, pointing out various contradictions he found in these works. He considered that some of the mathematical devices Ptolemy introduced into astronomy, especially the equant, failed to satisfy the physical requirement of uniform circular motion, and wrote a scathing critique of the physical reality of Ptolemy's astronomical system, noting the absurdity of relating actual physical motions to imaginary mathematical points, lines and circles: [85]

Ptolemy assumed an arrangement (hay'a) that cannot exist, and the fact that this arrangement produces in his imagination the motions that belong to the planets does not free him from the error he committed in his assumed arrangement, for the existing motions of the planets cannot be the result of an arrangement that is impossible to exist… [F]or a man to imagine a circle in the heavens, and to imagine the planet moving in it does not bring about the planet's motion. [86][87]

In his Aporias against Ptolemy, Ibn al-Haytham commented on the difficulty of attaining scientific knowledge:

Truth is sought for itself [but] the truths, [he warns] are immersed in uncertainties [and the scientific authorities (such as Ptolemy, whom he greatly respected) are] not immune from error… [8]

He held that the criticism of existing theories—which dominated this book—holds a special place in the growth of scientific knowledge:

Therefore, the seeker after the truth is not one who studies the writings of the ancients and, following his natural disposition, puts his trust in them, but rather the one who suspects his faith in them and

questions what he gathers from them, the one who submits to argument and demonstration, and not to the sayings of a human being whose nature is fraught with all kinds of imperfection and deficiency. Thus the duty of the man who investigates the writings of scientists, if learning the truth is his goal, is to make himself an enemy of all that he reads, and, applying his mind to the core and margins of its content, attack it from every side. He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either prejudice or leniency. [8]

In his On the Configuration of the World, despite his criticisms directed towards Ptolemy, Ibn al-Haytham continued to accept the physical reality of the geocentric model of the universe, [90]presenting a detailed description of the physical structure of the celestial spheres in his On the Configuration of the World:

The earth as a whole is a round sphere whose center is the center of the world. It is stationary in its [the world's] middle, fixed in it and not moving in any direction nor moving with any of the varieties of motion, but always at rest. [91]

While he attempted to discover the physical reality behind Ptolemy's mathematical model, he developed the concept of a single orb (falak) for each component of Ptolemy's planetary motions. This work was eventually translated into Hebrew and Latin in the 13th and 14th centuries and subsequently had an influence on astronomers such as Georg von Peuerbach [1]during the European Middle Ages and Renaissance. [92][93]

Ibn al-Haytham's The Model of the Motions of Each of the Seven Planets, written in 1038, was a book on astronomy. The surviving manuscript of this work has only recently been discovered, with much of it still missing, hence the work has not yet been published in modern times. Following on from his Doubts on Ptolemy and The Resolution of Doubts, Ibn al-Haytham described the first non-Ptolemaic model in The Model of the Motions. His reform was not concerned with cosmology, as he developed a systematic study of celestial kinematics that was completely geometric. This in turn led to innovative developments in infinitesimal geometry. [94]

His reformed empirical model was the first to reject the equant [95]and eccentrics, [96]separate natural philosophy from astronomy, free celestial kinematics from cosmology, and reduce physical entities to geometric entities. The model also propounded the Earth's rotation about its axis, [97]and the centres of motion were geometric points without any physical significance, like Johannes Kepler's model centuries later. [98]

In the text, Ibn al-Haytham also describes an early version of Occam's razor, where he employs only minimal hypotheses regarding the properties that characterize astronomical motions, as he attempts to eliminate from his planetary model the cosmological hypotheses that cannot be observed from the Earth. [99]

Ibn al-Haytham distinguished astrology from astronomy, and he refuted the study of astrology, due to the methods used by astrologers being conjectural rather than empirical, and also due to the views of astrologers conflicting with that of orthodox Islam. [100]

was very remote from the earth and did not belong to the atmosphere." [104]He wrote that if the Milky Way was located around the Earth's atmosphere, "one must find a difference in position relative to the fixed stars." He described two methods to determine the Milky Way's parallax: "either when one observes the Milky Way on two different occasions from the same spot of the earth; or when one looks at it simultaneously from two distant places from the surface of the earth." He made the first attempt at observing and measuring the Milky Way's parallax, and determined that since the Milky Way had no parallax, then it does not belong to the atmosphere. [105]

In 1858, Muhammad Wali ibn Muhammad Ja'far, in his Shigarf-nama, claimed that Ibn al- Haytham wrote a treatise Maratib al-sama in which he conceived of a planetary model similar to the Tychonic system where the planets orbit the Sun which in turn orbits the Earth. However, the "verification of this claim seems to be impossible," since the treatise is not listed among the known bibliography of Ibn al-Haytham. [106]

In geometry, Ibn al-Haytham developed analytical geometry and established a link between algebra and geometry. [107]Ibn al-Haytham also discovered a formula for adding the first 100 natural numbers (which may later have been intuited by Carl Friedrich Gauss as a youth). Ibn al-Haytham used a geometric proof to prove the formula. [108]

His contributions to number theory includes his work on perfect numbers. In his Analysis and Synthesis, Ibn al-Haytham was the first to realize that every even perfect number is of the form 2 n−1(2 n− 1) where 2 n− 1 is prime, but he was not able to prove this result successfully (Euler later proved it in the 18th century). [5]

Ibn al-Haytham solved problems involving congruences using what is now called Wilson's theorem. In his Opuscula, Ibn al-Haytham considers the solution of a system of congruences,

and gives two general methods of solution. His first method, the canonical method, involved Wilson's theorem, while his second method involved a version of the Chinese remainder theorem. [5]

In psychology and musicology, Ibn al-Haytham's Treatise on the Influence of Melodies on the Souls of Animals was the earliest treatise dealing with the effects of music on animals. In the treatise, he demonstrates how a camel's pace could be hastened or retarded with the use of music, and shows other examples of how music can affect animal behaviour and animal psychology, experimenting with horses, birds and reptiles. Through to the 19th century, a majority of scholars in the Western world continued to believe that music was a distinctly human phenomenon, but experiments since then have vindicated Ibn al-Haytham's view that music does indeed have an effect on animals. [113]

In early Islamic philosophy, Ibn al-Haytham's Risala fi’l-makan (Treatise on Place) presents a critique of Aristotle's concept of place (topos). Aristotle's Physics stated that the place of something is the two-dimensional boundary of the containing body that is at rest and is in contact with what it contains. Ibn al-Haytham disagreed and demonstrated that place (al- makan) is the imagined three-dimensional void between the inner surfaces of the containing body. He showed that place was akin to space, foreshadowing René Descartes's concept of place in the Extensio in the 17th century. Following on from his Treatise on Place, Ibn al- Haytham's Qawl fi al-Makan (Discourse on Place) was a treatise which presents geometric demonstrations for his geometrization of place, in opposition to Aristotle's philosophical concept of place, which Ibn al-Haytham rejected on mathematical grounds. Abd-el-latif, a supporter of Aristotle's philosophical view of place, later criticized the work in Fi al-Radd ‘ala Ibn al-Haytham fi al-makan (A refutation of Ibn al-Haytham’s place) for its geometrization of place. [84]

Ibn al-Haytham also discussed space perception and its epistemological implications in his Book of Optics. His experimental proof of the intromission model of vision led to changes in the way the visual perception of space was understood, contrary to the previous emission theory of vision supported by Euclid and Ptolemy. In "tying the visual perception of space to prior bodily experience, Alhacen unequivocally rejected the intuitiveness of spatial perception and, therefore, the autonomy of vision. Without tangible notions of distance and size for correlation, sight can tell us next to nothing about such things." [116]

Ibn al-Haytham wrote a work on Islamic theology, in which he discussed prophethood and developed a system of philosophical criteria to discern its false claimants in his time. [122]He also wrote a treatise entitled Finding the Direction of Qibla by Calculation, in which he discussed finding the Qibla, where Salah prayers are directed towards, mathematically. [101]

Therefore, the seeker after the truth is not one who studies the writings of the ancients and, following his natural disposition, puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them, the one who submits to argument and demonstration, and not to the sayings of a human being whose nature is fraught with all kinds of imperfection and deficiency. Thus the duty of the man who investigates the writings of scientists, if learning the truth is his goal, is to make himself an enemy of all that he reads, and, applying his mind to the core and margins of its content, attack it from every side. He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either prejudice or leniency. [8]

In The Winding Motion, Ibn al-Haytham further wrote that faith (or taqlid "imitation") should only apply to prophets of Islam and not to any other authorities, in the following comparison between the Islamic prophetic tradition and the demonstrative sciences:

From the statements made by the noble Shaykh, it is clear that he believes in Ptolemy's words in everything he says, without relying on a demonstration or calling on a proof, but by pure imitation (taqlid); that is how experts in the prophetic tradition have faith in Prophets, may the blessing of God be upon them. But it is not the way that mathematicians have faith in specialists in the demonstrative sciences. [126]

Ibn al-Haytham described his search for truth and knowledge as a way of leading him closer to God:

I constantly sought knowledge and truth, and it became my belief that for gaining access to the effulgence and closeness to God, there is no better way than that of searching for truth and knowledge. [127]

According to medieval biographers, Ibn al-Haytham wrote more than 200 works on a wide range of subjects, [73]of which at least 96 of his scientific works are known. Most of his works are now lost, but more than 50 of them have survived to some extent. Nearly half of his surviving works are on mathematics, 23 of them are on astronomy, and 14 of them are on optics, with a few on other subjects. [129]Not all his surviving works have yet been studied, but some of the ones that have are given below. [101][130]

4. ^ (Hamarneh 1972): A great man and a universal genius, long neglected even by his own people. (Bettany 1995): Ibn ai-Haytham provides us with the historical personage of a versatile universal genius.

14. ^ (Rashed 2007, p. 19): "In his optics ‘‘the smallest parts of light’’, as he calls them, retain only properties that can be treated by geometry and verified by experiment; they lack all sensible qualities except energy."

27. ^ ab(Wade & Finger 2001): "The principles of the camera obscura first began to be correctly analysed in the eleventh century, when they were outlined by Ibn al-Haytham."

28. ^ abc(Salam 1984): Ibn-al-Haitham (Alhazen, 965–1039 CE) was one of the greatest physicists of all time. He made experimental contributions of the highest order in optics. He enunciated that a ray of light, in passing through a medium, takes the path which is the easier and 'quicker'. In this he was anticipating Fermat's Principle of Least Time by many centuries. He enunciated the law of inertia, later to become Newton's first law of motion. Part V of Roger Bacon's "Opus Majus" is practically an annotation to Ibn al Haitham's Optics.

40. ^ (Briffault 1928, p. 190–202): What we call science arose as a result of new methods of experiment, observation, and measurement, which were introduced into Europe by the Arabs. […] Science is the most

momentous contribution of Arab civilization to the modern world, but its fruits were slow in ripening. Not until long after Moorish culture had sunk back into darkness did the giant to which it had given birth, rise in his might. It was not science only which brought Europe back to life. Other and manifold influences from the civilization of Islam communicated its first glow to European life. […] The debt of our science to that of the Arabs does not consist in startling discoveries or revolutionary theories; science owes a great deal more to Arab culture, it owes its existence…The ancient world was, as we saw, pre-scientific. The astronomy and mathematics of Greeks were a foreign importation never thoroughly acclimatized in Greek culture. The Greeks systematized, generalized and theorized, but the patient ways of investigations, the accumulation of positive knowledge, the minute methods of science, detailed and prolonged observation and experimental inquiry were altogether alien to the Greek temperament. […] What we call science arose in Europe as a result of new spirit of enquiry, of new methods of experiment, observation, measurement, of the development of mathematics, in a form unknown to the Greeks. That spirit and those methods were introduced into the European world by the Arabs.

41. ^ (Sarton 1927), "The Time of Al-Biruni": [Ibn al-Haytham] was not only the greatest Muslim physicist, but by all means the greatest of mediaeval times. Ibn Haytham's writings reveal his fine development of the experimental faculty. His tables of corresponding angles of incidence and refraction of light passing from one medium to another show how closely he had approached discovering the law of constancy of ratio of sines, later attributed to Snell. He accounted correctly for twilight as due to atmospheric refraction, estimating the sun's depression to be 19 degrees below the horizon, at the commencement of the phenomenon in the mornings or at its termination in the evenings. (cf. (Dr. Zahoor & Dr. Haq 1997))

42. ^ (Elliott 1966), Chapter 1: Alhazen was one of the ablest students of optics of all times and published a seven-volume treatise on this subject which had great celebrity throughout the medieval period and strongly influenced Western thought, notably that of Roger Bacon and Kepler. This treatise discussed concave and convex mirrors in both cylindrical and spherical geometries, anticipated Fermat's law of least time, and considered refraction and the magnifying power of lenses. It contained a remarkably lucid description of the optical system of the eye, which study led Alhazen to the belief that light consists of rays which originate in the object seen, and not in the eye, a view contrary to that of Euclid and Ptolemy.